Most men with an elevated blood level of total prostate-specific antigen (PSA)—the most common trigger for biopsy in US men—do not have prostate cancer. As a result, it has been estimated that there are close to 750,000 unnecessary prostate biopsies each year in the US. There is considerable evidence that measuring the isoforms of PSA separately, rather than combining them together in a single measure of total PSA, can help predict the presence of prostate cancer. These data include studies showing that cancer is predicted by free PSA, BPSA or −2proPSA. Indeed, free PSA is often measured separately, with urologists given results in terms of total PSA and free-to-total PSA ratio, with an estimated 10 million free PSAs measured per year. There is also evidence that hK2, the molecule that converts PSA from its pro- to active form, is informative of prostate risk. However, none of these markers on their own constitute good predictors of prostate biopsy outcome.
There have been several attempts to build predictive models for prostate cancer, most notably the “Prostate Cancer Prevention Trial Risk Calculator”, the “Sunnybrook”, and the European Randomized trial of Screening for Prostate Cancer (ERSPC) risk calculator. The problem with these models is that they require more or less extensive clinical work-up, that is, the patient needs to visit a urologist. For instance, the ERSPC risk calculator requires data on prostate volume, which is obtained by inserting an ultrasound probe into the rectum. Accordingly, new methods and apparatuses for predicting risk of prostate cancer and/or prostate gland volume would be beneficial.